It is known to provide optical communications networks having multiple nodes coupled by links. Many topologies are conceivable. A ring type of topology has always been the primary choice for fiber-based metropolitan area networks (MAN), because such a topology can help minimize fiber deployment costs, and simplify routing, control, and management issues. Such issues become more important in networks having multiple optical channels such as wavelengths. It is known to provide dynamic routing of such lightpaths through the network to try to match rapid changes in demand. To provide bandwidth on demand a network should have a fast set up time, a fair blocking probability independent of number of spans of a desired path, and a good bandwidth efficiency. Many approaches have been conceived for solving this routing and wavelength assignment (RWA) challenge. They can be categorized as either centralized or distributed approaches. An example of a distributed approach is a token passing scheme to avoid contention for network resources. A particular type of this is a multitoken protocol for networks having multiple optical channels.
As new applications and services such as video on demand (VoD), video broadcasting, and IP telephony, take an increasing share of the capacity, the MAN traffic characteristics, in terms of both required bandwidth and quality of service (QoS) assurance are tending to change. VoD and video broadcasting are characterized by large and strongly asymmetrical bandwidth requirements, because the majority of the traffic takes origin from a video server and is directed downstream to the client nodes. In this context, important QoS constraints include low average and maximum latency. This is due to the fact that even though VoD can tolerate a latency slightly higher than strictly real time traffic thanks to buffering, once in playback that latency must remain confined in tight boundaries in order to avoid buffer overflow or starvation. It is likely that such video-related traffic will exceed best effort traffic in terms of required bandwidth, hence the interest of many network operators to effectively accommodate QoS traffic in their MANs.
Given this context, multi-token protocols for WDM optical packet ring have good characteristics of flexibility and performance to support the requirements of QoS sensitive traffic. In multi-token rings, the time is not slotted. For each wavelength channel, there is a special control packet, i.e., the token, which travels around the ring, allowing exclusive access to the given optical channel by the node currently holding the token.
As described in more detail in U.S. Pat. No. 7,092,633, multitoken architectures have the advantage of seamlessly supporting variable length packets and guaranteeing both fairness and bounded latency, thanks to the limited token holding time. Notably to handle on demand traffic, such as VoD, such multitoken architectures can help enable a good balance between the three requirements of fast set up time for optical connections or lightpaths, fair blocking probability and good bandwidth efficiency.